Cases of Nipah infection have been found in Kerala again, after two people were confirmed to have died of the viral disease in Kozhikode district. Two others, aged nine and 24, are under treatment. They are family members of the first victim, who died on August 30.
Kerala health Minister Veena George held a high-level meeting to review the situation in Kozhikode on Tuesday morning. Union Health minister Mansukh Mandaviya said a central team of experts has been sent to the state.
While the Nipah virus does not spread as quickly as the Covid-19 virus, it is more deadly. According to the World Health Organization (WHO), the overall global case fatality rate of Nipah is estimated at 40% to 75% .
What is the Nipah virus infection?
Nipah is a zoonotic disease, which means it is transmitted to humans through infected animals or contaminated food. It can also be transmitted directly from person to person through close contact with an infected person, the WHO says. Its symptoms, according to the US Centers for Disease Control and Prevention (CDC), fever, headache, cough, sore throat, difficulty in breathing, and vomiting.
In severe cases, disorientation, drowsiness, seizures, encephalitis (swelling of the brain) can occur, progressing to coma and death.
How is Nipah transmitted?
The first outbreaks of the Nipah virus among humans was reported from Malaysia (1998) and Singapore (1999). The virus takes its name from the village in Malaysia where the person in whom the virus was first isolated died of the disease.
The transmission from animals happens mainly through consumption of contaminated food. According to the CDC, transmission can happen due to “consumption of raw date palm sap or fruit that has been contaminated with saliva or urine from infected bats. Some cases of NiV [Nipah] infection have also been reported among people who climb trees where bats often roost.”
The animal host reservoir for this virus is known to be the fruit bat, commonly known as flying fox. Fruit bats are known to transmit this virus to other animals like pigs, and also dogs, cats, goats, horses and sheep.
Humans get infected mainly through direct contact with these animals, or through consumption of food contaminated by saliva or urine of these infected animals. But human-to-human transmission is also considered possible. The CD says “person-to-person spread of NiV is regularly reported in Bangladesh and India. This is most commonly seen in the families and caregivers of NiV-infected patients, and in healthcare settings.”
Since it was first identified in 1998-99, there have been multiple outbreaks of the Nipah virus, all of them in South and Southeast Asian nations. In Bangladesh, there have been at least 10 outbreaks since 2001.
In India, West Bengal had seen an outbreak in 2001 and 2007, while Kerala had reported several cases in 2018, and isolated cases in 2019 and 2021.
How fast does the Nipah virus spread?
The Nipah virus is known to spread far more slowly than SARS-CoV-2. However, it is its ability to kill that is the biggest concern. During the first outbreak in Bengal’s Siliguri in 2001, 45 of the 66 people confirmed to have been infected died. That is a mortality rate of 68%. In the next outbreak, in Nadia district of West Bengal, in 2007, all the five infected people died.
During the 2018 outbreak in Kerala in 2018, 17 of the 18 patients confirmed to have been infected died.
In the Malaysian outbreak in 1999, a total of 265 people had been found infected, of whom 105 had died, according to a study, ‘Nipah Virus: Past Outbreaks and Future Containment’, by researchers from Cochin University of Science and Technology published in the April 2020 issue of the journal Viruses.
However, so far, all outbreaks of the Nipah virus have been localised and contained relatively quickly. One of the main reasons for a relatively quick end to an outbreak is the fact that Nipah virus is not very infectious and human-to-human transmission is not very easy.
A study by Bangladeshi researchers P Devnath of Noakhali Science and Technology University and H M A A Masud of Chittagong University, published in 2021, noted that the reproductive number (R0) in the previous outbreaks of Nipah virus was about 0.48. The R-value is a measure of how quickly the virus spreads in the population. A value less than one means less than one person is being infected by an already infected person. In such a scenario, the outbreak is expected to diminish relatively quickly.
Further, the very high death rates also contribute to low transmission.
Casualty department converted to an Isolation Ward for patients suspected with Nipah virus at Kalamassery medical College in Ernakulam district, in 2019. (Express file photo by Nirmal Harindran) 
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